The present invention relates to a coaxial engine starter for an internal combustion engine.
FIG. 1 is a cross section of an example of a conventional engine starter which includes a front bracket 1 mounted on an engine side and forming an outer wall of the starter, an output shaft 2 having a front end portion rotatably supported by a bearing 3 of the front bracket 1, an over-running clutch 4 slidably inserted axially into the output shaft 2, an armature shaft 7, an internal gear 8, a planet gear device 9 to be meshed with the internal gear 8, an electromagnetic switch 10 for controlling a current to be supplied to the starter and moving the over-running clutch 4 forwardly (rightwardly), a lever 11 for transmitting the movement of the electromagnetic switch 10 to the over-running clutch 4 , a yoke 12 of the starter, a rear bracket 13 and bolts 14 for fixedly securing the front bracket 1, the yoke 12 and the rear bracket 13, all together. The over-running clutch 4 includes a clutch-outer 4a having a spline 5, a clutch-inner 4b having a pinion 6 and a roller 4c disposed between the clutch-outer 4a and the clutch-inner 4b. The armature shaft 7 includes a gear 7a and the latter, the internal gear 8 and the planet gear device 9 constitute a planet reduction gear machanism for reducing a rotational speed of the armature shaft 7.
In the conventional engine starter constructed as mentioned above, the rotational force of the armature shaft 7 is normally transmitted through the planet reduction gear mechanism to the output shaft 2 and then through the pinion 6 formed on a front portion of the clutch-inner 4b of the over-running clutch 4 and meshed with the spline 5 of the output shaft 2 to a ring gear (not shown) of the engine to start the latter. Immediately after a starting of the engine, a rotational force of the engine is transmitted through the ring gear to the pinion 6, so that the rotational speed of the pinion 6 together with the output shaft 2 is increased. Upon such increase of the rotational speed of the pinion 6, which results in a disengagement of the clutch-inner 4b of the over-running clutch 4 due to an action of the roller 4c, causes the pinion 6 to rotate freely to thereby cut the rotational force applied from the engine to the pinion 6 off.
Since the conventional engine starter includes two shafts 2 and 7, a layout thereof with respect to the engine is relatively difficult. Further, since the front bracket 1 must be machined engine by engine, the manufacturing cost becomes considerable. In addition thereto, there is a problem of eccentricity of the pinion 6 of the over-running clutch 4 due to the fact that vibration or shock on the side of the engine is transmitted to the front bracket 1 connected directly thereto.